You could quickly drill a small hole in each case, in order to fit a tall button like this one: https://www.sparkfun.com/products/8605 https://www.sparkfun.com

You could quickly drill a small hole in each case, in order to fit a tall button like this one: https://www.sparkfun.com/products/8605 https://www.sparkfun.com/products/8605 Also, there's some U2F devices that trigger the approval simply when they are plugged in.